Secado de café pergamino por lecho fluidizado con asistencia de microondas

Tradicionalmente el secado del café pergamino húmedo en Colombia, se realiza por secado solar y aire caliente. El tiempo, temperatura, color del grano y principalmente el contenido de humedad final entre 10-12% b.h. se utilizan para establecer el punto final del proceso. Se estudiaron los cambios en las características físicas y parámetros hidrodinámicos del café pergamino húmedo en lecho fluidizado y secado por microondas, utilizando un diseño factorial 32 (velocidad del aire: 2, 4 y 6 m/s con 50, 80 y 100% de potencia del microondas) hasta alcanzar el nivel de humedad final. La fluidización se obtiene circulando aire al sector de secado a través de una placa (33 cm x 32 cm) con un tamaño de orificios de 5 mm con una distancia entre ellos de 7 mm (2116 orificios). En el sector de secado, el producto en estado fluidizado, fue irradiado mediante un magnetrón (1000 W). La mejor condición es: velocidad del aire de 4 m/s con 100% de potencia del microondas en 72 minutos, con una reducción del contenido de humedad hasta 11,3% b.h. La difusividad efectiva varió entre 9,19x10-12 y 1,33x10-11 m2/s. La energía de activación y factor pre-exponencial se determinó como 2,9 W/g y 2x10-10 m2/s.Traditionally drying of wet parchment coffee in Colombia, it is by solar drying and hot air. Time, temperature, grain color and mainly the final moisture content between 10-12% w.b. are used to set the end point of the process. The changes were studied in the physical characteristics and hydrodynamic parameters of wet parchment coffee in fluidized bed and microwave drying by using a factorial design 32 (air speed: 2, 4 and 6 m/s with 50, 80 and 100% microwave power) until reach the final moisture level. The fluidization is obtained by circulating air to the drying sector through a plate (33 cm x 32 cm) with a size of holes 5 mm with a distance between them of 7 mm (2116 holes). In the drying sector, the product in the fluidized state, was irradiated by a magnetron (1000 W). The best condition is air velocity of 4 m/s with 100% microwave power for 72 minutes, with moisture content 11.3% w.b. The effective diffusivity varied between 9.19x10-12 and 1.33x10-11 m2/s. The activation energy and pre-exponential factor for moisture diffusion was determined as 2.9 W/g y 2x10-10 m2/s.Centro de Investigación y Desarrollo en Criotecnología de Alimento

Numerical solution of coupled mass and energy balances during osmotic microwave dehydration

The mass and energy transfer during osmotic microwave drying (OD-MWD) process was studied theoretically by modeling and numerical simulation. With the aim to describe the transport phenomena that occurs during the combined dehydration process, the mass and energy microscopic balances were solved. An osmotic-diffusional model was used for osmotic dehydration (OD). On the other hand, the microwave drying (MWD) was modeled solving the mass and heat balances, using properties as function of temperature, moisture and soluble solids content. The obtained balances form highly coupled non-linear differential equations that were solved applying numerical methods. For osmotic dehydration, the mass balances formed coupled ordinary differential equations that were solved using the Fourth-order Runge Kutta method. In the case of microwave drying, the balances constituted partial differential equations, which were solved through Crank-Nicolson implicit finite differences method. The numerical methods were coded in Matlab 7.2 (Mathworks, Natick, MA). The developed mathematical model allows predict the temperature and moisture evolution through the combined dehydration process.Facultad de Ingenierí